1. Field of the Invention
The present invention relates to a new process for the preparation of a substantially improved rabies vaccine having a high content of active substance in proportion to contaminating proteins and fats, i.e., a particularly high specific activity, and to the vaccine thus obtained.
2. Description of the Prior Art
Rabies vaccines have hitherto been obtained from the brains of rabbits, rats or mice, in which the viruses have been multiplied in the living animal by direct intracerebral inoculation of rabies viruses of standardized seed strains. Various disadvantages are associated with these processes:
1. The veruses are grown in the living animal, which is exposed to great suffering during the procedure and finally must be sacrificed. PA0 2. The inoculation of the living animal, the keeping of the animals and the harvesting of the viruses from their brains cannot take place under such completely hygienically perfect and sterile conditions as, for example, in the case of multiplication of the viruses in vitro or in the egg. PA0 3. The removal of the brain of rabbits, rats or mice a few days old requires a very difficult and troublesome operation technique. In addition, with the smallness and viscous consistency of these brains, the losses of brain matter are considerable. PA0 4. The viruses grown in living animals are contaminated with proteins which have a relatively high content of myelin, a protein-containing substance, which, when the vaccine is used, gives rise to side-reactions which can increase to encephalitis. The myelin content can be reduced, but not avoided, by using very young animals which are only a few days old for multiplication of the virus.
An improvement has been achieved by multiplying the rabies viruses in duck embryos. On the one hand, the use of living animals is thereby avoided, and on the other hand, the content of myelin in embryonal tissue is relatively low, if this compound is present at al.
Nevertheless, the rabies vaccine obtained from duck embryos still has considerable disadvantages compared with the ideal vaccine. The virus suspension obtained from the embryos contains a high proportion of proteins which, because of the nature of the suspension of cells and viruses, cannot be separated or can only be incompletely separated in an economic manner by known methods. The higher the protein content of vaccines, the higher the occurrence of undesirable side reactions when the vaccine is used. On repeated vaccination, which is essential for certain professional people, such as, hunters, foresters, and veterinary surgeons, these side reactions can increase to violent allergic defense reactions against the foreign protein.
A better vaccine can be achieved by multiplication of rabies viruses in virto in human diploid cell cultures. In this context, see H. Koprowski, Laboratory Techniques in Rabies by M. M. Kaplan and H. Koprowski, WHO Monograph Series No. 23, Chapter 28, pages 256-60 (1973): Vaccine for man prepared in human diploid cells; T. J. Wiktor, Develop. biol. Standard, Volume 37, pages 265-66, S. Karger, Basle 1978: Production and control of rabies vaccines made on diploid cells; and T. J. Wiktor et al, Develop. biol. Standard, Volume 40, pages 3-9 (1978): Development and clinical trial of rabies vaccine of tissue culture.
The vaccine thus obtained contains, as an impurity, human proteins which produce less side reactions than foreign proteins.
A considerable disadvantage of this method is the relatively low rate of multiplication of the rabies viruses on diploid fibroblast cells, which makes 10- to 25-fold concentrations necessary for the preparation of the vaccine. This method is thus not efficient enough to meet the world-wide demand for rabies vaccine within the scope of the economic possibilities.